fix: add app/src to embedded Python ._pth for module discovery

Windows embedded Python ignores PYTHONPATH when a ._pth file exists.
Add ../app/src to the ._pth so wled_controller is importable.
Fixes ModuleNotFoundError on portable builds.

build-dist.ps1

@@ -106,6 +106,11 @@ $pthContent = $pthContent -replace '#\s*import site', 'import site'
 if ($pthContent -notmatch 'Lib\\site-packages') {
     $pthContent = $pthContent.TrimEnd() + "`nLib\site-packages`n"
 }
+# Embedded Python ._pth overrides PYTHONPATH, so add the app source path
+# directly for wled_controller to be importable
+if ($pthContent -notmatch '\.\.[/\\]app[/\\]src') {
+    $pthContent = $pthContent.TrimEnd() + "`n..\app\src`n"
+}
 Set-Content -Path $pthFile.FullName -Value $pthContent -NoNewline
 Write-Host "  Patched $($pthFile.Name)"